In summary (thanks, Wowhead!):
- You can loot three bosses once a day. For level 110 120 players they drop gear of ilevel 900 350 (or higher).
- Players level 60 and up can loot them - they (and their loot) scale.
- Each day there are three bosses up. Two of these are up every day:
- Lord Kazzak in the Blasted Lands
- Azuregos in Azshara.
The third is one of the four old green dragon bosses that guarded the portals to the Dream. These will vary daily - either :
- A bunch of their loot has looks that are available from other sources in the game, but some of it is unique. Perculia (see the link to the Wowhead page) has marked items with unique looks with an asterisk, but I've also summarized it in a list at the end of this post.
- There's an associated daily quest, The Originals, and a breadcrumb quest given when you open your Anniversary Gift from the mail. The daily awards 50 Timewarped Badges and may be picked up from Historian Ju'pa in The Valley of Spirits, Orgrimmar or Historian Llore in Stormwind Library. If you did the anniversary daily quiz last year, you may remember the locations. The quest-givers offer that daily again this year, as well, so you can earn 75 badges a day from the two dailies.
- The quest-givers also sell some goggles for transmog: Bronze-tinted Sunglasses. They cost 200 badges, which happens to be how many badges are in your Anniversary Gift. You can save the badges on your main and just buy the glasses on an alt. The quest-givers also sell some consumables that give you temporary disguises/costumes. I won't list them all.
Summary of the loot with unique transmog appearances
The bosses drop plenty more loot than what is listed below, but the following are supposed to have looks that have no other available source - at least according to the Wowhead page. Please let us know if you find any additions or corrections.
[table=border:1px solid #CDBEE9; background-color:#e9f6f9; border-collapse:collapse;color:#2e8949;padding:5px 10px;][tr][td=2,]Lord Kazzak[/td][/tr]
[tr][td]Amberseal Keeper[/td][td]two-handed staff[/td][/tr]
[tr][td]Empyrean Demolisher[/td][td]one-handed mace (agi / str)[/td][/tr]
[tr][td=2,]Azuregos[/td][/tr]
[tr][td]Acid Inscribed Pauldrons[/td][td]plate shoulders (str / int)[/td][/tr]
[tr][td]Unmelting Ice Girdle[/td][td]plate waist (str / int)[/td][/tr]
[tr][td]Fang of the Mystics[/td][td]dagger (int)[/td][/tr]
[tr][td]Typhoon[/td][td]two-handed sword (str)[/td][/tr]
[tr][td=2,]Green Dragons (apparently loot is shared between all four)[/td][/tr]
[tr][td]Circlet of Restless Dreams[/td][td]leather head (agi / int)[/td][/tr]
[tr][td]Deviate Growth Cap[/td][td]leather head (agi / int)[/td][/tr]
[tr][td]Unnatural Leather Spaulders[/td][td]leather shoulders (agi / int)[/td][/tr]
[tr][td]Dragonspur Wraps[/td][td]leather wrists (agi / int)[/td][/tr]
[tr][td]Boots of Fright[/td][td]leather feet (agi / int)[/td][/tr]
[tr][td]Leggings of the Demented Mind[/td][td]mail legs (agi / int)[/td][/tr]
[tr][td]Boots of the Endless Moor[/td][td]mail feet (agi / int)[/td][/tr]
[tr][td]Acid Inscribed Pauldrons[/td][td]plate shoulders (str / int)[/td][/tr]
[tr][td]Gauntlets of the Shining Light[/td][td]plate hands (str / int)[/td][/tr]
[tr][td]Acid Inscribed Greaves[/td][td]plate feet (str / int)[/td][/tr]
[tr][td]Hammer of Bestial Fury[/td][td]one-handed mace (agi / str)[/td][/tr]
[tr][td]Nightmare Blade[/td][td]one-handed sword (agi / str)[/td][/tr]
[tr][td]Polished Ironwood Crossbow[/td][td]crossbow[/td][/tr][/table]